Ultrahigh frequency magnetron oscillator



C. W. HANSELL ULTRAHIGH FREQUENCY MAGNETRQN OSCILLATQR Dec. 28,v 1.93.7.

Filed June 13, 1935 2 Sheets-Sheet l CLARENCE w. H ANSELL #S .4MM

ATTORNEY Dec. 28, 1937. 4 c. w. HANsELL 2,103,352

ULTRAHIGH FREQUENCY MAGNETRON scILLAToR` Filed June l5, 1935 2Sheets-Sheet 2l /IUMBZE METAL 703/176 SL /DEH /Mwmrpn INVENTOR CLARENCEW. HANSE-iv..

ATTO R N EY Patented 28, 1937 sacaste ULTRAHIGH FREQUENCY MAGNEOSCILLATR Clarence W. Hansell, Port dene-reen, N. Y., as-

le'nor to Radio Corporation ci erica, a corporation of Delaware iApplication .lune i3, 11.933, derlei No. 075.5311

1c Claims.

This invention relates to the production of ultra high frequencyoscillations in electron discharge devices and, more particularly, tosuch of these devices wherein the traveling electrons them- 5 selves andthe consequent space charges about the electrodes of' the devices areprimarily responslble for the regeneration required to produceoscillations.

In my United States Patent No. 2,011,133, l0 granted May 14, 1935, thereis disclosed a method of producing ultra high frequency oscillations bya whistle eiect in a solid anode magnetron. In this magnetron oscillatorthere is provided a small central filament which is surrounded by a positively charged cylindrical anode. A magnetic held is applied to thespacebetween the iilament and the anode having flux lines parallel tothe filament. Under these circumstances electrons are pulled out fromthe filament toward the anode, but due to the action of. the magneticeld a considerable portion of them do not reach the anode and are causedto turn around and return to the vicinity of the filament. Thesereturning electrons build up a space charge around the filament whichprevents new electrons from coming out until those which previously leftthe filament have returned to it. The controlling eiiect of thereturning electrons gives a sort of regeneration or whistle eiect whichcauses oscillations to take place irrespective of adjustment of theelectrode circuits, although this effect may be increased if thecircuits are properly tuned so that fluctuations in anodel to cathodepotential m assist in producing iiuctuations in the number of this typeof magnetron oscillator the frequency produced corresponds to the periodrequired for an electron to traverse the curved path from the filamentto the anode and back again.

u present invention which, however, provides a path for the electrons totravel over which is only about half as long as that described above andin this manner is believed to produce a frequency about twice is high asthat obtained in the aforementioned arrangement. In addition to thiswhistle effect, the present invention also obtains regeneration througha time delay phenomena due to the finite velocities of the electronsthemselves, a mode of operation which is described in my United StatesPatent No. 2,009,369, granted July 23, 1935.

In my last mentioned patent there is disclosed an electron dischargedevice'oscillator which has an anode substantially a half wave lengthylong,

electrons leaving the vicinity of the cathode. In

The foregoing whistle effect is utilized in the` (Cl. 25d-36) the waveiength taken corresponding to the frequency of the desired oscillations.During oscillation one-half of the anode is arranged to be at a mazdm'umpotential when the other half is at a minimum potential. inasmuch as theanode 6 transfers potential waves at the velocity of light, and theelectrons in traveling through the cathode anode space have a much loweraverage velocity, it will be seen that the time required for theelectrons to reach the anode will be substantially equal to the timerequired for the anode tov reverse its radio frequency potential. Thatportion of the anode which is at a maximum potential will thus tend toattract the electrons toward it, and by suitable dimensioning of thetube will be made to be at a minimum potential when the electronsimpinge thereon, thereby establishing the necessary condition forsustained oscillation generation. There is thus obtained an electrondischarge device in which potentials on different portions of the anodeuctuate in such a manner that after a certain portion has experienced amaximum potential sufiicient to start a cloud of electrons toward itfrom the cathode, the voltage on that portion will have changed as theelectrons are about to lmpinge thereupon with the result that thefluctuations in anode potential cause regeneration and sustainedoscillation without the necessity for potential fluctuations of acontrol element or grid as ordinarily used. It is this time delay effectwhich is combined with the electron whistle eiect to aid in producingoscillations in the present invention.

In the above two types of oscillators described in my United Statespatents, supra the amount oi. power obtainable is limited by/theemission from the illament and by the maximum power dissipationallowable at the anode. The present .invention overcomes thisdisadvantage and makes possible the production of higher power not onlyby obtaining greater emission, but also by increasing the anodedissipation. At the same time the frequency'of the oscillations producedin accordance with the present invention is increased by reversing thedirection of the electron travel.

A feature of this invention is the novel type of magnetron used in whichthe cathode is in the form of a cylinder and the anode in the form of athin tube at the center of the cylindrical lelectron emitting element,and it is by means of this novel construction that the length of thepath traveled by the electrons per cycle is only half as ,greatv as inthe case of a solid anode magnetron. Consequently, for substantially the55 same anode voltage the oscillator in accordance with the presentinvention will produce a fref quency approximately twice as high as thatdescribed in the prior methods.

'I'he invention, of course, is not limited to the use of a cylindricalcathode since it will be obvious that, if desired, a plurality offilaments in parallel spaced equally on a ring of a predetermineddiameter may be used to surround a central metal rod anode axiallypositioned with respect to said ring.

Referring to the drawings, Figure 1 represents schematically atransverse section of a well known type of magnetron showing the pathstaken by the electrons, and Figure 2 shows schematically a transversesection of the magnetron in accordance with the present invention alsoillustrating the paths taken by the traveling electrons., Figure 3illustrates, partly in section and partly schematically, a preferredarrangement of a magnetron oscillator in accordance with the presentinvention. Figure 4 shows a modification of the present inventionwherein there is utilized a three electrode tube for controlling theoscillator. Figure 5 showsgraphically the variations in anode to cathodepotential across tube of Figure 4 with respect to time. Figure 6illustrates another modification of thepresent invention with means formodulating the output of the oscillator, and Figure 7 shows graphically,in a manner similar to Figure 5, the variations in potential across tubeof Figure 6.

In Figure 1 is shown schematically a known type of magnetron oscillatoras described in my United States Patent No. 2,001,133, supra,cornprising an electron emitting cathode element I and a cylindricalanode 2 to which the electrons are attracted. This gure showsapproximately the path which the electrons take at a critical platevoltage for a definite strength magnetic field set up coaxially with thecathode and at right angles to the plane of the ilgure by a field coil,not shown. 'Ihe complete path of the electronic stream from cathode toanode and back to the cathode is approximately that of a cardioid asshown in the drawings. If the anode voltage is increased all of theelectrons will be attracted to the anode and if the field strength isincreased none of the electrons will strike the anode. At a criticalvalue determined by the anode voltage and the strength of the magneticeld some of the electrons will return to the cathode and will describe apath approximately that of the cardioid indicated.

Figure 2 shows the paths of the electrons in the oscillator of thepresent invention wherein the outside cylinder 3 is caused to be theelectron emitting cathode element while the relatively small diameterelement 4 insidevthe cathode is used as an anode. It will be quiteevident'that in this case the length of the path traveled by theelectrons per cycle is less than half as great as in the case of thesolid cylindrical anode magnetron shown in Figure l. Consequently, forsubstantially the same anode voltage the new oscillator shown in Figure2 produces a frequency about twice as high as that shown in Figure 1.

Figure 3 illustrates the preferred embodiment of the present inventionwherein there is shown an oscillator comprising an envelope 5,preferably of glass 0r quartz, having surrounding it a metal shield 6and within it a cylindrical cathode I which has at the ends thereofshielding members 8, vwhich approach more closely to a centrally locatedanode 9 than does the electron emitting surface. The object of usingthese shielding members is to obtain more nearly parallel motion of theelectrons and, therefore, greater oscillation energy. Anode 9 which ismaintained at a positive potential from the positive terminal of thehigh voltage rectifier through the medium of a metal tubing I3 connectedto the anode and an adjustable slider i5 is also in the form of acylinder and is preferably cooled by a stream of gas or liquid so thatit will stand high energy dissipation. This cooling fluid may besupplied through a rubber hose I0 and passed out of the anode through arubber hose II,.both of which connect with the anode through metal'tubes I2 and I3 respectively. There is thus provided through the centerof the vacuum tube an anode consisting of a small tube through which acooling fluid such as water or oil or any gaseous cooling medium, suchas hydrogen or air, is circulated. The anode is tuned by means ofadjustable tuning sliders I4 and I5 on the metal tubes, and when theoscillator isA operated with circuits tuned to the fundamental frequencythe distance from the center of the anode to each of the adjustabletuning sliders will be approximately onequarter of the wave length orodd multiples thereof. Sliders I4 and I5 are in contact with both theanode 9 and the horizontal metal plate 34 which is mounted on supports,as shown.

Horizontal plate 34 is in contact with metallic shield 6 surrounding theenvelope 5. This manner of operation utilizes the presence of standingwaves on the metal tubes connected to the anodes.

'I'he cylindrical cathode 'I encircling the anode is provided withenergy from a power supply source 35 through transformer I6 and overleads I1 and I8 for heating the cylinder to a temperature suilicientlyhigh to cause it to emit a considerable number of electrons. Thecylinder may be made of thin metal through which a large heating currentis passed at a low potential or, if desired, it may be of the heatertype in which the electron emitting material is indirectly heated bymeans of a metal wire wound aboutit on a suitable form of refractorymaterial in the manner commonly employed for indirect cathode heating invacuum tubes. Preferably the cathode and its connections are also tunedfor the operating frequency and this may be done by varying the lengthof the heating current supply leads from the cathode to a point ofsubstantially' zero potential. If desired, a slider arrangement such asI9, I9 may be used for adjustment. It is preferred, however, that theadjustment be made in the cathode heating leads in the beginning fortuninglapproximately to the desired frequency after which all tuning innormal operation may be done by means of the anode sliders It and I5. Inthe drawings,` the output circuit has been shown, for purposes ofillustration only, as a transmission line 20 capacitively coupled to theoscillator and extending to an antenna or radiator 2l. This radiator ispreferably of a directive type. The simple radiator has been shown onlyfor the purpose of illustration. Trombone slides 22 have been indicatedfor tuning the transmission line to the desired frequency in cases wherethe antenna does not match the characteristic impedance of the line.

Two iield coils 23, 23 are shown provided for setting up an intensemagnetic eld between the vacuum tube electrodes in the directionparallel to the axis of the tube.

Although it is believed that the presence of the magnetic eld willimprove the power eiiiciency and make oscillations more certain, it willbe understood that in some instances the use of a. magnetic field may beundesirable. In such case its use may be eliminated. For example, in atransmitter used for airplanes the weight of a field coil and the powersupply for energizing it will be considerable and for this reason it maybe desirable to use either no magnetic field or a relatively weak eld tosave weight.

The operation of the oscillator in Figure 3 in producing oscillations issubstantially as follows:

The electrons emitted from the cylindrical cathode 'I will be propelledtoward the fluid cooled central anode upon the occurrence of a positivepotential thereon and these electrons will travel toward the anode withincreasing velocity. Simultaneously with their movement toward the anodethe electrons are subjected to the influence of the magnetic eldparallel to the axis of the tube due to the energization of field coils23, 23, and for a certain value of iield a large portion of electronsattracted to the anode 8 will not reach it, but will be deiiectedsuiciently to pass close to it and return again to the vicinity of thecathode, as shawn ln Figure 2.

If the flow of a large number of electrons is started toward the anode 9their arrival inthe Avicinity of the anode will set up a negative spacecharge around it which will balance out the inuence of the anodepotential upon the electron emitting surface and no more electrons willbe pulled out of the cathode 'I until thosel already in the spacebetween the anode and the cathode have completed their travel past theanode and are returning again to the cathode. As soon as all of theelectrons in the space have left the vicinity of thev anode, theelectrostatic attraction at the cathode will again become effective anda new group of electrons will start out. action, recurring at intervalscorresponding to the time of the travel of the electrons, is equivalentto a radio frequency oscillation, energy from which is taken out bytuning and coupling any suitable utilization circuit, such as atransmission line. 20 andantenna 2|, to the anode cathode circuit. Ifthe electrode circuits are tuned, such as by adjustable sliders Iii, Iand tuning elements I9, I9, the action of the tube in producingoscillations may be considerably increased, although in this case it maybe necessary to make some readjustment in the anode potential. This willbe evident from the mere observation that the arrival of the groups ofelectrons in the vicinity of the anode is accompanied by the impact ofsome of the electrons upon the anode surface, the total number of theimpacting electrons corresponding to the D. C. input current. Theseimpacting electrons, in combination with oscillations in the anodecircuit, serve to reduce the anode potential during the time when it isdesired to have a minimum number of electrons leaving the cathode. Ahalf cycle later, at the time when maximum emission from the cathode isdesired, the anode will have oscillated to a maximum positive potentialof a value greater than the direct current potential by an amountcorresponding to thestrength of the oscillations on the anode. It willthus be seen that there is obtained a cooperative effect between theelectron whistle principle and the emitter of electrons.

This

time delay principle, both of which are described above in connectionwith my United States patents, supra.

Figure 4 illustrates another embodiment of the present invention whereina three element vacuum tube 24, having an anode 33, a grid 2I and acathode 39, is used to control the production of oscillations in theoscillator 25. In this figure controltube 24 has a low resistance mostof the time so that the voltage on the oscillator tube is equal to thatexisting between terminals B and C of] the anode current supply source26, less the relatively small voltage drop in the control tube. Asindicated in the drawings, this voltage may be of the order of 2000volts. Under such conditions there will be suiiicient current and anodePower lost in the oscillator tube 25 to heat the anode 36 to atemperature where it become's an Then, periodically, the control tube iscaused to cut oi its current by having the potential on its grid 2lswing negative whereupon the voltage impressed upon the oscillator tube25 is that between terminals A and B of supply source 20, less somecurrent voltage drop due to the resistance 28 in series with the lead toterminal A, in this case around 1000 volts. The voltage applied to theoscillator tube from terminals A'and B is arranged to be opposite inpolarity from that previously applied from terminals B and C. Thus, thecathode 40 of the tube 25 will be made positive and, due to the emissionfrom the anode l36 of tube 25, a reversed current will ow in the tube.This, it will be seen, is the precise condition required for setting uposcillations in the manner previously described in connection withFigures 2 and 3, provided all other conditions and adjustments have beenpreviously made. Thus there may be employed an ordinary vacuum tube foroscillator 25 by passing current through it in a normal directionsuiliclent to heat the anode until it will emit electrons and thenreversing the anode to cathode potential. By rapidly reversing the p0-tentials, modulated ultra high f'. equency oscillations can be produced.The relatively small proportion of the time during which oscillationstake place keeps the average energy dissipation on the small centralportion of the tube within its energy dissipation limits, otherwise theconditions for obtaining any oscillations at all might betoo severe forthe tube towithstand.

Commutator 29, which is driven, by means not shown, over its driveshaft, is illustrated in the drawings, `by way of example only, as oneway of controlling the potential on the grid 21 of the control tube 24whereby there is caused the desired condition for oscillations to occurat short periods at a rate determined by the Commutator. For commercialpurposes it would probably be necessary that the condition foroscillations occur at the rate of from 250 to 2500 times per second orhigher, whereas for testing purposes interruptions at the rate of 120per second or so would be in order. In the latter case anelectromagnetic relay may be used.

The brush arrangement shown for connecting the grid 21 of tube 24 to thebias source of potential 32 is one which is adequately described inUnited States Patent No. 1,963,587, granted June 19, 1934, to Richard E.Mathes. In. this arrangement the brushes are short circuited by thecommutator bars extending longitudinally of the revolving drum atintervals depending upon the speed of the drum and the width of thebars. By making the brushes movable along the commutator and by taperingthe width of the bars any desired relative length of time for potentialsin one direction or the other may be readily obtained. l

Figure 5 illustrates diagrammatically the variations in anode to cathodepotential of tube 25 with respect to time. In this gure thel positivepotential sign indicates the condition for heating the anode of the tubeand the negative potential sign indicates the condition for reversingthe functions of anode and cathode to produce oscillations.

In Figure 6 there is shown a two electrode, tube 30, having an anode 31and a cathode 38, which may be used as a magnetron oscillator havingmagnetic flux parallel to the axis of the tube provided by coils in amanner indicated in Figure 3. This magnetron will give oscillations whenthe cathode 38 is positive with respect to the anode 31 of the tube. Theanode 31 is heated by electron bombardments from the D. C. voltage andcurrent until it becomes an emitter of electrons,

at which time suilicient keyed or modulated alternating current voltageis superimposed upon the direct current voltage to cause a reversal ofthe anode-cathode voltage for part of the time. The ultra high frequencyoscillations will thus take vplace during the interval of reversepotential. For utilization purposes there is shown an antenna 3l whichis electromagnetically coupled to the anode lead of tube 30. Theoperation of the circuit, it is thought, will be obvious from theforegoing description.

Figure 7 indicates the variations in potential across the tube 30 inFigure 6, with respect to time in the same way that Figure 5 illustratedthe potential across tube 25 in Figure 4.

It will, of course, be understood that this new type of oscillatorhereinabove described may be modulated by varying its electrodepotentials or the strength of magnetic field by any of the means alreadywell known in the art. The output of the circuit may, if desired, alsobe modulated by variably absorbing the output energy, or by Varyingimpedances in the output circuits in .known manner. In practice, any ofthese modulating means may be employed, according to servicerequirements.

I claim:

1. An oscillation generator comprising an electron discharge devicehaving a cylindrically shaped electron emitting element, a source ofheating energy for said element and leads extending from said source tosaidelement, an electron collecting element at the center of theelectron emitting element and positioned along the axis thereof, andmeans for tuning said leads and the eifective length of said electroncollecting member.

2. An oscillation generator system comprising an electron dischargedevice having a cylindrically shaped electron emitting element, a sourceof heating energy for said element and leads extending frcm said sourceto said element, and an electron collecting element at the center of theelectron emitting element and positioned along the axis thereof, meansfor tuning each of said leads and for making the eifective length ofsaid collecting member to be an odd multiple of half the wave generatedby said system, and means for producing a magnetic field having uxparallel to the axis of the emitting element.

3. An oscillation generator system comprising Within an envelope anelectron discharge device having a solid cylindrical cathode, a rod-likeanode axially positioned in the center of said. cathode and along theaxis thereof, a shield surrounding said envelope, and a tuning sliderconnected with each end of said anode and said shield for tuning saidanode, whereby the distance from the center of said anode to each slideris approximately an odd multiple of a quarter wave length When saidsystem is tuned to the fundamental frequency.

4. An oscillation circuit comprising an electron discharge device havinga cylindrical cathode, an anode axially positioned in the center of saidcathode and extending lengthwise on both sides of said cathode, metallictubular conductors connected to both ends of said anode, means forcausing the presence of standing waves thereon, said means includingmetal sliders in contact with said tubular conductors and in circuitwith said cathode for tuning the eifective lengths of said tubularconductors, whereby the frequency of the oscillations generated may bechanged.

5. The combination with an oscillation circuit comprising an electrondischarge device having a solid cylindrical cathode of appreciable Widthand a, concentrically positioned rod-like anode at the axis of saidcathode, of means for cooling said anode, and means for adjustablytuning the effective length of said anode.

6. The combination with an oscillation circuit comprising an electrondischarge device having an envelope, a hollow cylindrical cathode ofimperforate material Within said envelope and an anode tubeconcentrically positioned along the axis of said cathode, of metallictubing connecting with both ends of said anode and extending outside ofsaid envelope for enabling the existence of standing Waves on saidmetallic tubing, tuning elements for said anode located on said metaltubing and coupled back to said cathode, andr a utilization circuitcapacitively coupled to said anode.

7. The combination with an oscillation circuit comprising an electrondischarge device having an envelope, a hollow cylindrical cathode ofimperforate material within said envelope and an anode tubeconcentrically positioned along the axis of said cathode, of metallictubing connecting with both ends of said anode and extending outside ofsaid envelope for enabling the existence of standing waves on saidmetallic tubing, tuning elements for said anode located on both sides ofsaid cathode and approximately an odd multiple of a. quarter wave lengthfrom the center of said anode, said elements being connected to saidtubing and coupled back to said cathode, and a utilization circuitcoupled to said anode.

8. In an electron discharge device oscillator having a cathode and ananode, the method of generating oscillations which includes attractingelectrons from said cathode to portions of the anode only at times when'the portions are subjected to a maximum anode potential, decreasing theanode potential on the portions as the electrons arrive, andperiodically interrupting the stream of electrons.

9. In an electron discharge device oscillator having a cathode and ananode, the method of generating oscillations which includes propellingelectrons from said cathode to portions of said anode only at times whenthe portions are subjected to a maximum anode potential, decreasing theanode potential on the portions as the electrons arrive, periodicallyinterrupting the stream of electrons, and generating a magnetic eld todeflect the path of the electrons.

10. In an electron discharge device, the com- @,id v f tential to saidanode with respect to said cath- 4 suitable polarizing potential to theother of said electrodes with respect to said cathode, in order to heatsaid other electrode to enable same to emit electrons, the method ofproducing oscillations which includes reversing the polarization of saidelectrodes whereby the direction of current ow from the other electrodeto the cathode simultaneously reverses.

12. In combination,` an electron discharge device having an anode and acathode, another device having an anode, cathode and control electrode,the anode of said last device being connected to the cathode of saidfirst device, a source of potential having positive and negative termi-'nais and a third terminal, the potential between said negative andthird terminals being greater than the potential between said positiveand third terminals, a connection including a resistance from saidpositive terminal to the anode of said last device, a direct connectionfrom the anode of said rst device to the third terminal oi' said-source,a connection including al resistance from said positive terminal to saidcontrol electrode, a connection from said negative terminal to thecathode of said second device, and means for periodically applying anegative bias to the control electrode of said second device wherebysaid last device is made inoperative.

13. In anl electron discharge device oscillator having an anode and acathode substantially concentrically positioned with respect to eachother, and means for applying a suitable polarizing poode to heat saidanode to enable same to emit electrons, the method of producingoscillations which includes periodically reversing the polarization ofsaid anode and cathode at an audio frequency rate of at least 250 timesper second,

whereby the directionl of current dow from the anode to the cathode isreversed. at said rate.

14. An electron discharge device having an inner cathode and an outeranode surrounding said cathode, a source of energy for maintaining saidanode at a positive potential relativeA to said cathode for causing saidanode to be heated to emit electrons, and means including switchingmechanism for reversing the relative polarities of said anode andcathode whereby electrons ow from said anode to said cathode.

15. In combination, a magnetron oscillator i having a cathode and ananode within an envelope and an external magnetic eld surrounding saidenvelope, a source of potential between-said anode land cathode formaintaining said anode at a potential sulciently positive relative tosaid cathode to enable said anode to be heated to emit electrons, andperiodically operating keying mechanism including another source ofpotential for superimposing energy uponvthe circuit connections fromsaidanode and cathode to said rst source of a` value suiilciently highto cause a reversal of the relative polarities of said electrodes.whereby electrons emanating from said anode are collected by saidcathode.

16. An oscillation generator comprising an electron discharge devicehaving means substantially arranged in the ,form of a hollow cylinderfor emitting electrons, a source of heating energy and .leads extendingfrom said source to said means,

an electron collecting element at the center of said means andpositioned substantially along the axis thereof, and means for tuningsaid leads and the eiective length oi' said electron collecting element.

CLARENCE W. HANSELL.

